$2.$
$\frac{x+3}{2007}$ - $\frac{x+3}{2008}$ = $\frac{x+3}{2010}$ - $\frac{x+3}{2009}$
$⇒$ $\frac{x+3}{2007}$ - $\frac{x+3}{2008}$ - $\frac{x+3}{2010}$ + $\frac{x+3}{2009}$=$0$
$⇔$ ($x+3$).$\frac{1}{2007}$ - $\frac{1}{2008}$ - $\frac{1}{2010}$ + $\frac{1}{2009}$ = $0$
$⇔$ ($x+3=0$) (do $\frac{1}{2007}$ - $\frac{1}{2008}$ - $\frac{1}{2010}$ + $\frac{1}{2009}$ > $0$
$⇒$ $x=-3$
$\text{Bài 1}$: